James Chisum is 28, lean, vegan and, from all appearances, entirely healthy; a cliff-diving, four-times-per-week exerciser who hasn’t seen a doctor in many years -- and who has no plans to go anytime soon.

Chisum doesn’t drink, doesn’t smoke and doesn’t believe men his age should have yearly medical check-ups. In fact, they should try to stay out of the health care system altogether, he argues. They should strive to maintain their vigor but let doctors “who are already extremely overworked” spend their precious time treating sick people.

“The fact that annual (physicals) have become a cultural norm speaks more to our increasingly sedentary lifestyles and the standard American diet,” said Chisum, who works in marketing and lives in southern California. “Annual physicals are actually included in my insurance. I don't use them because I feel like it's a burden on the system for something that I don't view as a necessity.”

Meet one of the scores of American men, although, arguably one of the healthier guys on the list, who simply refuse to go to the doctor, ever, either out of male pride, out of white-coat fear or simply out of lifestyle habit.

"Many [adult] men go to the doctor for the first time in their 40s — on a stretcher with a heart attack,” says Dr. Ridwan Shabsigh, head of the International Society of Men’s Health and a urologist in New York City.

At least 40 percent of men in their 40s have never had a cholesterol test and one-third refuse to go for annual check-ups, according to Shabsigh.

While new research suggests that annual exams do little good for healthy people and screening tests once regularly given during yearly physicals -- prostate-specific antigen (PSA) blood tests, for example -- are no longer recommended by the United States Preventive Services Task Force, there's a clear and worrying trend among adult men: a higher rate of adult women than guys are routinely seeing medical professionals for preventative visits, Shabsigh said.

“If you look deeper into this – it’s fascinating. If you look at the data by gender, before the age of 18, the utilization of health care is equal by gender. After age 18, there is a dramatic reduction in health-service utilization by males,” Shabsigh said. “Now, why is there no gender discrepancy before age 18? Mom. Mom takes both boys and girls equally to the doctor. After age 18, boys disappear.

The same phenomenon even holds truth for oral care, the society found: Men go for dental-maintenance visits less often than women.

One leading theory on why some males avoid the doctor centers around certain “cultural myths that men are the stronger sex (which sends an erroneous message to other guys) that they do not need to be concerned – and should not be concerned – about their health,” said Will Courtenay, author of “Dying to be Men: Psychosocial, Environmental, and Biobehavioral Directions in Promoting the Health of Men and Boys.” He also is a psychologist in Oakland, Calif.

Shabsigh said he sees this same misconception in his practice, including some men who have binged on alcohol so heavily while they were college students, they have developed sexual dysfunctions in their 20s. They consider themselves bulletproof -- too tough to get sick. And that's an old way of thinking for the males.

"When a boy cries, the mother and father come in and say, 'You are a young man, don’t cry.' When a girl cries, they hug her and say, 'Don’t worry.' So the man is toughened," Shabsigh said. "Maybe that toughening has the side effect of when you are older and you’re a man you don’t run for the doctor for every little cry."

Some men also seem more inclined than women to believe that they're invulnerable to health risks, including cancer, Courtenay contends.

That mindset could be genetic, a DNA strand leftover from ancient human communities that relied on physically stronger males to jeopardize their health while hunting wild game, experts suggest.

“Maybe men are evolutionary different, biologically different; a woman is more caring and a man is more risk taking,” Shabsigh said.

For some guys like Mark Brown, 52, a Las Vegas resident, purposely staying away from the doctor ultimately cost him.

“I was raised believing that men do not go to doctors,” Brown said. “About 15 years ago, I came down with a terrible head cold and sinus infection. At the time, I was traveling a lot between Las Vegas and Washington, D.C. so I was in airplanes every week. By the time I went to the doctor, the infection had moved into my right ear and ultimately caused complete deafness in the ear.

“So, I used to be one of the tough guys but today at the first sign of illness, I high-tail it down to the doctor's office,” Brown said.

Back in Southern California, Chisum remains unconvinced that doctor-led prevention is vital in keeping healthy.

“I think that when I was younger, being a man may have played a role in my avoidance of doctors," Chisum said.

“But as I've matured and learned more about the health-care system, I feel my gender's role has taken a backseat to wisdom about personal responsibility and empowerment,” he added. “I don't foresee changing my stance.”

But even guys who feel fine, need to see a health care provider regularly, if only to avoid unpleasant surprises.

Most people who have high blood pressure don't know it, according to the National Institutes of Health. It's the same with high blood sugar and high cholesterol -- the conditions often don't have any symptoms until the disease becomes advanced. The only way to know is to get checked.

Men over age 34 should be checked for high cholesterol and heart disease every 5 years. A preventive health visit should be every 2 years until age 50, and then once a year. For screening recommendations, go to the United States Preventive Services Task Force website.